The invention relates generally to engine bearing vibration signatures, and more particularly to a sampling and acceleration enveloping technique for enhancing differential bearing damage signatures associated with engine differential bearings.
Differential bearings are some of the most vulnerable parts of an engine and are also some of most difficult parts of an engine for which to monitor the operational condition.
Vibration signatures provide the most reliable early warning data associated with regular rolling-element bearing systems. In that regard, the acceleration enveloping based technique has existed for many years. The synchronous sampling technique is also widely used in bearing signature enhancement, especially in variable speed applications.
Synchronous sampling is a technique for converting equal time sampling to equal shaft circumferential angle sampling, so that the rotor speed dependency is eliminated. This is usually achieved by installing an encoder on to the bearing which is used to monitor the shaft operation by counting the physical events of the rotating part passing through a stationary detector.
Both bearing races in a differential bearing operation however, are in motion, and the race speeds are usually not accurately controlled during bearing operations. Further, the differential bearing assembly is buried under other mechanical components; and the bearing signatures are proportional to the speed difference between the races. Synchronous sampling therefore is required to extract the inherently small and speed difference dependent signatures. Encoders for the differential speed are not physically feasible for a differential bearing due to the moving races.
It would be advantageous to provide a sampling technique that overcomes the disadvantages described above associated with traditional sampling techniques for ascertaining differential bearing damage signatures during bearing operations.